FIGS. 10 and 11 are plan and side views, respectively, of a conventional actuator. As shown in these figures, this actuator has head suspensions (support springs) 23 each supporting a magnetic head 21 at one end thereof and fixing arms 25 each having the other end of the head suspension 23 fixed thereto, and is provided with a carriage 27 attached to a disk unit in such a way as to be turnable around a shaft hole 28. A moving coil 29 disposed in the magnetic circuit of the disk unit for giving a turning force to the carriage 27 according to the applied electric current is fixed to the carriage 27. The head suspensions 23 are fixed to the corresponding fixed arms 25 with the aid of fixing members 31, respectively. The fixing arms 25 are made of a metal such as aluminum, while the head suspensions 23 are made of stainless steel.
As shown in FIG. 12, each fixing member 31 has a cylindrical portion 33 thrusted through the through-holes of both the head suspension 23 and the fixing arm 25, and a collar 35 provided at one end thereof. The head suspension 23 is fixed to the fixing arm 25 by outwardly bending the end portion of the cylindrical portion 33 as shown in FIG. 12, or by pressing the inner wall of the cylindrical portion 33 toward the inner wall of the through-hole of the fixing arm 25 in the direction of the arrows as shown in FIG. 13. The collar 35 fixes the head suspension 23 toward the fixing arm 25.
In the foregoing conventional example, the head suspension 23, the fixing arm 25 and the cylindrical portion 33 are each made of a metal, and the diameter of the cylindrical portion 33 is only a little smaller than the diameter of the through-hole of the fixing arm 25. Accordingly, the head suspension 23 can be easily and strongly superposed on and joined to the fixing arm 25 even though the cylindrical portion 33 is pressed from the inner side thereof to deform the wall of the cylindrical portion 33 as shown in FIG. 13.
On the other hand, for example, U.S. Pat. No. 5,382,851 discloses an actuator wherein a read/write head is installed in an aperture of a metallic insert member of a flat plate form embedded in a resin arm molded by insert molding with the insert member being inserted into the resin arm. Only the end portion of this insert member, opposite to the head, is embedded in the arm.
In general, an injected molten resin is of course brought into contact with an insert member in the case of insert molding. Since, however, a resin generally exhibits no affinity for a metal, causes shrinkage at the time of solidification of the resin in a molten state and has other inconvenient properties, gaps will sometimes be formed between the insert member and the resin when the resulting molding is solidified. The gaps prevent close adhesion of the resin to the insert member to cause backlash or play of the insert member. Such backlash, in other words, relative positional deviation between the insert member and the resin, is usually slight. Depending on the characteristics required of an apparatus wherein such a molding is used, however, such backlash poses problems in some cases.
Among others, when only one end portion of the insert member is embedded in the resin as in the actuator of the above-mentioned U.S. Patent, the influences of the gaps are large because the gaps between the resin and the insert member are localized only in that one end portion. Such gaps may cause an error in the relative position of the head fixed in the insert member as against the arm. The accuracy of the position of the head is an important factor required of the actuator as a precision device.
Further, in the case of the above-mentioned U.S. Patent, the head is directly installed in the aperture of the insert member positioned at the tip of the resin arm. This involves a fear of making accurate read/write difficult because the contact pressure of the head to a disk is not constant.
Although it would also be possible to attach the head to the resin arm by utilizing a through-hole provided in the resin arm instead of using the insert member, direct joining of a metal to a resin does inevitably not attain an essentially strong bond unless an adhesive or the like is used therebetween.
In view of the foregoing problems of the prior art, an object of this invention is to enable joining between a metal plate and a resin plate with the aid of a fixing member to maintain a backlash-free accurate relative positional relationship between the metal plate and the resin plate. Another object of this invention is to provide a lightweight and high-precision swing-type actuator that does not cause any backlash between arms and head suspensions even when the arms are made of a resin. A further object of this invention is to enable the contact pressure of the head to a disk in a disk unit to be maintained constant.